P. Siegmann, L. Felipe-Sesé, F. D. Díaz Garrido, J. Pineiro-Ave
An optical non-contact and full-field system that allows large displacement measurements in x-, y- and z-direction is presented. The system combines 2-dimentional digital image correlation (for in-plane measurements) and fringe projection (for out-of-plane displacements) and uses only one camera. The in- and out-of-plane displacements are obtained at the same instant allowing real-time measurements thanks to a color encoding filtering procedure. The out-of-plane measurement allows the correction of the in-plane measurements and the system has to be precisely aligned by following an established alignment procedure. Furthermore, a calibration has to be done to obtain a fringe parameter k for each pixel of the specimen surface image necessary to relate the shifted phase with the out-of-plane displacements. The presented system obtains different values of k for each pixel because of the divergent and non-normal incidence of the fringe beam onto the sample surface (non zero incidence angle). The calibration is performed automatically and only has to be done once for each configuration of the system. The system is portable and can be easily adapted to measure large displacements and wide areas (using small incidence angle) or smaller distances but with higher resolutions (when increasing the incidence angle).
{"title":"An automated calibration system that combines fringe projection and 2D digital image correlation","authors":"P. Siegmann, L. Felipe-Sesé, F. D. Díaz Garrido, J. Pineiro-Ave","doi":"10.1117/12.2191110","DOIUrl":"https://doi.org/10.1117/12.2191110","url":null,"abstract":"An optical non-contact and full-field system that allows large displacement measurements in x-, y- and z-direction is presented. The system combines 2-dimentional digital image correlation (for in-plane measurements) and fringe projection (for out-of-plane displacements) and uses only one camera. The in- and out-of-plane displacements are obtained at the same instant allowing real-time measurements thanks to a color encoding filtering procedure. The out-of-plane measurement allows the correction of the in-plane measurements and the system has to be precisely aligned by following an established alignment procedure. Furthermore, a calibration has to be done to obtain a fringe parameter k for each pixel of the specimen surface image necessary to relate the shifted phase with the out-of-plane displacements. The presented system obtains different values of k for each pixel because of the divergent and non-normal incidence of the fringe beam onto the sample surface (non zero incidence angle). The calibration is performed automatically and only has to be done once for each configuration of the system. The system is portable and can be easily adapted to measure large displacements and wide areas (using small incidence angle) or smaller distances but with higher resolutions (when increasing the incidence angle).","PeriodicalId":212434,"journal":{"name":"SPIE Optical Systems Design","volume":"83 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2015-09-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129056860","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
M. Rossi, I. Ferrario, R. Ghislanzoni, P. Holbrouck, A. Ritucci, M. Taccola, M. Terraneo, F. Zocchi
In the framework of an European Space Agency contract, Media Lario Technologies is developing an optical payload for Earth Observation targeted to small satellites. In this paper we present a detailed description of the imager which, by leveraging on aspheric surfaces, bonnet polishing, lightweight materials, an off-the-shelf large format CMOS detector and multispectral filters integrated in the FPA, achieves remarkable image quality with compact volume claim and mass of only 15 kg. The instrument is based on a three mirror anastigmat (TMA) design with an aperture of 200 mm and an F/number of 6. The payload is designed to provide a ground sampling distance (GSD) of 2.75 m for the panchromatic channel at a reference altitude of 600 km, a field of view of 1° and a nominal MTF greater than 60% at Nyquist frequency with a Signal to Noise Ratio (SNR) greater than 100.
{"title":"Fabrication and testing of STREEGO: a compact optical payload for earth observation on small satellites","authors":"M. Rossi, I. Ferrario, R. Ghislanzoni, P. Holbrouck, A. Ritucci, M. Taccola, M. Terraneo, F. Zocchi","doi":"10.1117/12.2191285","DOIUrl":"https://doi.org/10.1117/12.2191285","url":null,"abstract":"In the framework of an European Space Agency contract, Media Lario Technologies is developing an optical payload for Earth Observation targeted to small satellites. In this paper we present a detailed description of the imager which, by leveraging on aspheric surfaces, bonnet polishing, lightweight materials, an off-the-shelf large format CMOS detector and multispectral filters integrated in the FPA, achieves remarkable image quality with compact volume claim and mass of only 15 kg. The instrument is based on a three mirror anastigmat (TMA) design with an aperture of 200 mm and an F/number of 6. The payload is designed to provide a ground sampling distance (GSD) of 2.75 m for the panchromatic channel at a reference altitude of 600 km, a field of view of 1° and a nominal MTF greater than 60% at Nyquist frequency with a Signal to Noise Ratio (SNR) greater than 100.","PeriodicalId":212434,"journal":{"name":"SPIE Optical Systems Design","volume":"27 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2015-09-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126323277","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
SiC mirrors are of excellent mechanical and thermal properties compared to their glass opponents. Efficient fabrication and testing of SiC mirrors, particularly the large freeform surfaces are very challenging. In this paper, direct CNC generation, deterministic polishing techniques including CCOS, MRF, and IBF were addressed in detail. Since testing is critical to make high accuracy freeform surfaces, the paper focused on Computer Generated Hologram (CGH) design and implement to measure large mirrors. In particular, detector to mirror mapping distortion was discussed in detail. Finally, some results for SiC mirrors were presented.
{"title":"Manufacturing and testing large SiC mirrors in an efficient way","authors":"Xuejun Zhang, Xuefeng Zeng, Haixiang Hu, Xiao Luo","doi":"10.1117/12.2189751","DOIUrl":"https://doi.org/10.1117/12.2189751","url":null,"abstract":"SiC mirrors are of excellent mechanical and thermal properties compared to their glass opponents. Efficient fabrication and testing of SiC mirrors, particularly the large freeform surfaces are very challenging. In this paper, direct CNC generation, deterministic polishing techniques including CCOS, MRF, and IBF were addressed in detail. Since testing is critical to make high accuracy freeform surfaces, the paper focused on Computer Generated Hologram (CGH) design and implement to measure large mirrors. In particular, detector to mirror mapping distortion was discussed in detail. Finally, some results for SiC mirrors were presented.","PeriodicalId":212434,"journal":{"name":"SPIE Optical Systems Design","volume":"14 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2015-09-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126563601","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
M. Ohlídal, I. Ohlídal, D. Nečas, J. Vodák, D. Franta, P. Nádaský, František Vižd'a
It is possible to encounter thin films exhibiting various defects in practice. One of these defects is area non-uniformity in optical parameters (e.g. in thickness). Therefore it is necessary to have methods for an optical characterization of nonuniform thin films. Imaging spectroscopic reflectometry provides methods enabling us to perform an efficient optical characterization of such films. It gives a possibility to determine spectral dependencies of a local reflectance at normal incidence of light belonging to small areas (37 μm × 37 μm in our case) on these non-uniform films. The local reflectance is measured by individual pixels of a CCD camera serving as a detector of an imaging spectroscopic reflectometer. It is mostly possible to express the local reflectance using formulas corresponding to a uniform thin film. It allows a relatively simple treatment of the experimental data obtained by imaging spectroscopic reflectometry. There are three methods for treating these experimental data in the special case of thickness non-uniformity, i.e. in the case of the same optical constants within a certain area of the film - single pixel imaging spectroscopic reflectometry method, combination of single-pixel imaging spectroscopic reflectometry method and conventional methods (conventional single spot spectroscopic ellipsometry and spectrophotometry), and multi-pixel imaging spectroscopic reflectometry method. These methods are discussed and examples of the optical characterization of thin films non-uniform in thickness corresponding to these methods are presented in this contribution.
{"title":"Possibilities and limitations of imaging spectroscopic reflectometry in optical characterization of thin films","authors":"M. Ohlídal, I. Ohlídal, D. Nečas, J. Vodák, D. Franta, P. Nádaský, František Vižd'a","doi":"10.1117/12.2191052","DOIUrl":"https://doi.org/10.1117/12.2191052","url":null,"abstract":"It is possible to encounter thin films exhibiting various defects in practice. One of these defects is area non-uniformity in optical parameters (e.g. in thickness). Therefore it is necessary to have methods for an optical characterization of nonuniform thin films. Imaging spectroscopic reflectometry provides methods enabling us to perform an efficient optical characterization of such films. It gives a possibility to determine spectral dependencies of a local reflectance at normal incidence of light belonging to small areas (37 μm × 37 μm in our case) on these non-uniform films. The local reflectance is measured by individual pixels of a CCD camera serving as a detector of an imaging spectroscopic reflectometer. It is mostly possible to express the local reflectance using formulas corresponding to a uniform thin film. It allows a relatively simple treatment of the experimental data obtained by imaging spectroscopic reflectometry. There are three methods for treating these experimental data in the special case of thickness non-uniformity, i.e. in the case of the same optical constants within a certain area of the film - single pixel imaging spectroscopic reflectometry method, combination of single-pixel imaging spectroscopic reflectometry method and conventional methods (conventional single spot spectroscopic ellipsometry and spectrophotometry), and multi-pixel imaging spectroscopic reflectometry method. These methods are discussed and examples of the optical characterization of thin films non-uniform in thickness corresponding to these methods are presented in this contribution.","PeriodicalId":212434,"journal":{"name":"SPIE Optical Systems Design","volume":"47 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2015-09-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114797488","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
CaF2 is one of the foremost optical materials used in ArF excimer laser optics. Surface quality of optically finished CaF2 plays an important role in the component’s lifetime. Several techniques were employed to assess surface quality of optically finished CaF2 in terms of top surface and subsurface damage, resulting in subsurface-damagefree CaF2. UV light and plasma interaction with CaF2 surfaces were investigated. The results were discussed in terms of surface roughness and cleanness associated with surface finishing and optical coatings.
{"title":"Surface assessment and mitigation of DUV optics","authors":"Jue Wang","doi":"10.1117/12.2190684","DOIUrl":"https://doi.org/10.1117/12.2190684","url":null,"abstract":"CaF2 is one of the foremost optical materials used in ArF excimer laser optics. Surface quality of optically finished CaF2 plays an important role in the component’s lifetime. Several techniques were employed to assess surface quality of optically finished CaF2 in terms of top surface and subsurface damage, resulting in subsurface-damagefree CaF2. UV light and plasma interaction with CaF2 surfaces were investigated. The results were discussed in terms of surface roughness and cleanness associated with surface finishing and optical coatings.","PeriodicalId":212434,"journal":{"name":"SPIE Optical Systems Design","volume":"57 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2015-09-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123966665","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
C. Wilde, F. Hahne, P. Langehanenberg, J. Heinisch
For the manufacturing of high performance optical systems, centered alignment of the optical surfaces within the assembly is becoming increasingly important. In this contribution, we will present a system for the automated alignment of optical surfaces for the high-throughput manufacturing of cemented doublets (and triplets) with optimized imaging performance. First of all, different concepts for the alignment of doublets etc. are discussed. Standard methods for cementing evaluate mechanical features, such as the outer barrel of one element as reference axis. Using this procedure the optical performance of the assembly that can be achieved is limited by imperfections in the collinearity of the element’s barrel axis and its optical axis. Instead, using the optical axis of the bottom element as target axis opens up perspectives for the production of multiplets with perfect symmetric imaging performance. For this concept, all three center of curvature positions of the optical surfaces are measured. Then, the top surface is aligned to the bottom element's optical axis using high-precision actuators. In order to increase the throughput of this procedure, the system is equipped with a novel measurement head that acquires autocollimation images of all three surfaces of a doublet at the same time. Thus, the positions of all surfaces are measured simultaneously during just a single rotation, avoiding both additional rotations and focus movements. Using this approach, cycle times can significantly be reduced from an average of 1 min to less than 10 seconds (w/o curing time). The system is reconfigurable in order to support a wide range of sample designs and enables cementing of high quality optics with centering errors below 2 μm.
{"title":"Reducing the cycle time of cementing processes for high quality doublets","authors":"C. Wilde, F. Hahne, P. Langehanenberg, J. Heinisch","doi":"10.1117/12.2196876","DOIUrl":"https://doi.org/10.1117/12.2196876","url":null,"abstract":"For the manufacturing of high performance optical systems, centered alignment of the optical surfaces within the assembly is becoming increasingly important. In this contribution, we will present a system for the automated alignment of optical surfaces for the high-throughput manufacturing of cemented doublets (and triplets) with optimized imaging performance. First of all, different concepts for the alignment of doublets etc. are discussed. Standard methods for cementing evaluate mechanical features, such as the outer barrel of one element as reference axis. Using this procedure the optical performance of the assembly that can be achieved is limited by imperfections in the collinearity of the element’s barrel axis and its optical axis. Instead, using the optical axis of the bottom element as target axis opens up perspectives for the production of multiplets with perfect symmetric imaging performance. For this concept, all three center of curvature positions of the optical surfaces are measured. Then, the top surface is aligned to the bottom element's optical axis using high-precision actuators. In order to increase the throughput of this procedure, the system is equipped with a novel measurement head that acquires autocollimation images of all three surfaces of a doublet at the same time. Thus, the positions of all surfaces are measured simultaneously during just a single rotation, avoiding both additional rotations and focus movements. Using this approach, cycle times can significantly be reduced from an average of 1 min to less than 10 seconds (w/o curing time). The system is reconfigurable in order to support a wide range of sample designs and enables cementing of high quality optics with centering errors below 2 μm.","PeriodicalId":212434,"journal":{"name":"SPIE Optical Systems Design","volume":"39 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2015-09-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115938936","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
K. Prater, J. Dukwen, T. Scharf, H. Herzig, S. Plöger, A. Hermerschmidt
Replication techniques for diffractive optical elements (DOEs) in soft materials such as plastic injection molding are state of the art. For precision glass molding in glasses with high transition temperatures, molds with extreme thermal resistivity, low chemical reactivity and high mechanical strength are needed. Glassy Carbon can be operated up to 2000°C making it possible to mold almost all glasses including Fused Silica with a transition temperatures above 1060°C. For the structuring of Glassy Carbon wafers photolithography and a RIE process is used. We have developed a process using Si as a hard mask material. If the flow rates of the etching gases O2 and SF6 are chosen properly, high selectivity of GC to Si 19:1 can be achieved, which provides excellent conditions to realize high resolution elements with feature size down to 1 micron and fulfills requirements for optical applications. We fabricated several multilevel GC molds with 8 levels of structuring. Two different optical functionalities were implemented: 6x6 array beamsplitter and 1x4 linear beamsplitter. The molds were applied for precision glass molding of a low Tg glass L-BAL 42 (from Ohara) with a transition temperature of 565°C. Their optical performance was measured. A more detailed analysis of the impact of mold fabrication defects on optical performance is done. Rigorous coupled wave analysis simulations are performed, where we included fabrication constrains such as duty cycle, edge depth errors, wall verticality and misalignment errors. We will compare the results with the design specifications and discuss the influence of fabrication errors introduced during the different process steps.
衍射光学元件(do)在软材料(如塑料注射成型)中的复制技术是最先进的。在高转变温度的玻璃中进行精密玻璃成型，需要极热阻、低化学反应性和高机械强度的模具。玻碳可以在2000°C的温度下工作，使得几乎所有的玻璃都可以成型，包括熔融二氧化硅，过渡温度高于1060°C。对于玻璃碳晶圆的结构，采用光刻和RIE工艺。我们已经开发了一种使用Si作为硬掩模材料的工艺。如果选择合适的蚀刻气体O2和SF6的流速，可以实现GC对Si 19:1的高选择性，这为实现特征尺寸小至1微米的高分辨率元件提供了良好的条件，满足了光学应用的要求。我们制作了多个8层结构的多层GC模具。实现了两种不同的光学功能:6x6阵列分光器和1x4线性分光器。将该模具应用于低Tg l - bal42玻璃(来自Ohara)的精密玻璃成型，过渡温度为565℃。测量了它们的光学性能。对模具制造缺陷对光学性能的影响进行了较为详细的分析。进行了严格的耦合波分析模拟，其中我们包括制造约束，如占空比，边缘深度误差，壁垂直度和不对中误差。我们将结果与设计规范进行比较，并讨论在不同工艺步骤中引入的制造误差的影响。
{"title":"Multilevel micro-structuring of glassy carbon molds for precision glass molding","authors":"K. Prater, J. Dukwen, T. Scharf, H. Herzig, S. Plöger, A. Hermerschmidt","doi":"10.1117/12.2191661","DOIUrl":"https://doi.org/10.1117/12.2191661","url":null,"abstract":"Replication techniques for diffractive optical elements (DOEs) in soft materials such as plastic injection molding are state of the art. For precision glass molding in glasses with high transition temperatures, molds with extreme thermal resistivity, low chemical reactivity and high mechanical strength are needed. Glassy Carbon can be operated up to 2000°C making it possible to mold almost all glasses including Fused Silica with a transition temperatures above 1060°C. For the structuring of Glassy Carbon wafers photolithography and a RIE process is used. We have developed a process using Si as a hard mask material. If the flow rates of the etching gases O2 and SF6 are chosen properly, high selectivity of GC to Si 19:1 can be achieved, which provides excellent conditions to realize high resolution elements with feature size down to 1 micron and fulfills requirements for optical applications. We fabricated several multilevel GC molds with 8 levels of structuring. Two different optical functionalities were implemented: 6x6 array beamsplitter and 1x4 linear beamsplitter. The molds were applied for precision glass molding of a low Tg glass L-BAL 42 (from Ohara) with a transition temperature of 565°C. Their optical performance was measured. A more detailed analysis of the impact of mold fabrication defects on optical performance is done. Rigorous coupled wave analysis simulations are performed, where we included fabrication constrains such as duty cycle, edge depth errors, wall verticality and misalignment errors. We will compare the results with the design specifications and discuss the influence of fabrication errors introduced during the different process steps.","PeriodicalId":212434,"journal":{"name":"SPIE Optical Systems Design","volume":"94 7 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2015-09-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127987208","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
V. Duma, G. Dobre, D. Demian, R. Cernat, C. Sinescu, F. Topala, M. Negruțiu, Gheorghe Huţiu, A. Bradu, J. Rolland, A. Podoleanu
As part of the ongoing effort of the biomedical imaging community to move Optical Coherence Tomography (OCT) systems from the lab to the clinical environment and produce OCT systems appropriate for multiple types of investigations in a medical department, handheld probes equipped with different types of scanners need to be developed. These allow different areas of a patient’s body to be investigated using OCT with the same system and even without changing the patient’s position. This paper reviews first the state of the art regarding OCT handheld probes. Novel probes with a uni-dimensional (1D) galvanometer-based scanner (GS) developed in our groups are presented. Their advantages and limitations are discussed. Aspects regarding the use of galvoscanners with regard to Micro-Electro- Mechanical Systems (MEMS) are pointed out, in relationship with our studies on optimal scanning functions of galvanometer devices in OCT. These scanning functions are briefly discussed with regard to their main parameters: profile, theoretical duty cycle, scan frequency, and scan amplitude. The optical design of the galvoscanner and refractive optics combination in the probe head, optimized for various applications, is considered. Perspectives of the field are pointed out in the final part of the paper.
{"title":"Handheld probes and galvanometer scanning for optical coherence tomography","authors":"V. Duma, G. Dobre, D. Demian, R. Cernat, C. Sinescu, F. Topala, M. Negruțiu, Gheorghe Huţiu, A. Bradu, J. Rolland, A. Podoleanu","doi":"10.1117/12.2191130","DOIUrl":"https://doi.org/10.1117/12.2191130","url":null,"abstract":"As part of the ongoing effort of the biomedical imaging community to move Optical Coherence Tomography (OCT) systems from the lab to the clinical environment and produce OCT systems appropriate for multiple types of investigations in a medical department, handheld probes equipped with different types of scanners need to be developed. These allow different areas of a patient’s body to be investigated using OCT with the same system and even without changing the patient’s position. This paper reviews first the state of the art regarding OCT handheld probes. Novel probes with a uni-dimensional (1D) galvanometer-based scanner (GS) developed in our groups are presented. Their advantages and limitations are discussed. Aspects regarding the use of galvoscanners with regard to Micro-Electro- Mechanical Systems (MEMS) are pointed out, in relationship with our studies on optimal scanning functions of galvanometer devices in OCT. These scanning functions are briefly discussed with regard to their main parameters: profile, theoretical duty cycle, scan frequency, and scan amplitude. The optical design of the galvoscanner and refractive optics combination in the probe head, optimized for various applications, is considered. Perspectives of the field are pointed out in the final part of the paper.","PeriodicalId":212434,"journal":{"name":"SPIE Optical Systems Design","volume":"31 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2015-09-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127304431","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
When using the BRDF to learn about surface statistics or to estimate hemispherical scatter from in-plane measurements the assumption is usually made that the surface is isotropic. Unfortunately, this is often not the case; for example a diamond turned mirror is not isotropic. Other common examples are rolled surfaces and situations where scatter is mostly caused by small discrete surface features such as scratches, pits or particles. Another example is scatter from an extended edge that is much longer than the illuminated spot. In these situations the measurements may be made differently and quantified in different units (such as area/sr or 1/deg instead of the common 1/sr associated with BRDF) in order to have a result that can reliably characterize the scatter source. The situation is further complicated by the fact that the popular stray radiation codes accept scatter data only in the standardized BRDF format with units of 1/sr. This paper reviews these situations for both measurement and analysis issues.
{"title":"Measuring and quantifying scatter from a variety of sample types","authors":"J. Stover","doi":"10.1117/12.2190986","DOIUrl":"https://doi.org/10.1117/12.2190986","url":null,"abstract":"When using the BRDF to learn about surface statistics or to estimate hemispherical scatter from in-plane measurements the assumption is usually made that the surface is isotropic. Unfortunately, this is often not the case; for example a diamond turned mirror is not isotropic. Other common examples are rolled surfaces and situations where scatter is mostly caused by small discrete surface features such as scratches, pits or particles. Another example is scatter from an extended edge that is much longer than the illuminated spot. In these situations the measurements may be made differently and quantified in different units (such as area/sr or 1/deg instead of the common 1/sr associated with BRDF) in order to have a result that can reliably characterize the scatter source. The situation is further complicated by the fact that the popular stray radiation codes accept scatter data only in the standardized BRDF format with units of 1/sr. This paper reviews these situations for both measurement and analysis issues.","PeriodicalId":212434,"journal":{"name":"SPIE Optical Systems Design","volume":"55 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2015-09-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133543897","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
M. Campos-García, Cesar Cossio-Guerrero, O. Huerta-Carranza, V. Moreno-Oliva
In this work we report the design of a null-screen for corneal topography. To avoid the difficulties in the alignment of the test system due to the face contour (eyebrows, nose, or eyelids), we design a conical null-screen with a novel radial points distribution drawn on it in such a way that its image, which is formed by reflection on the test surface, becomes an exact array of circular spots if the surface is perfect. Additionally, an algorithm to compute the sagittal and meridional radii of curvature for the corneal surface is presented. The sagittal radius is obtained from the surface normal, and the meridional radius is calculated from a function fitted to the derivative of the sagittal curvature by using the surfacenormals raw data. Experimental results for the testing a calibration spherical surface are shown. Also, we perform some corneal topography measurements.
{"title":"Advances in corneal topography measurements with conical null-screens","authors":"M. Campos-García, Cesar Cossio-Guerrero, O. Huerta-Carranza, V. Moreno-Oliva","doi":"10.1117/12.2192137","DOIUrl":"https://doi.org/10.1117/12.2192137","url":null,"abstract":"In this work we report the design of a null-screen for corneal topography. To avoid the difficulties in the alignment of the test system due to the face contour (eyebrows, nose, or eyelids), we design a conical null-screen with a novel radial points distribution drawn on it in such a way that its image, which is formed by reflection on the test surface, becomes an exact array of circular spots if the surface is perfect. Additionally, an algorithm to compute the sagittal and meridional radii of curvature for the corneal surface is presented. The sagittal radius is obtained from the surface normal, and the meridional radius is calculated from a function fitted to the derivative of the sagittal curvature by using the surfacenormals raw data. Experimental results for the testing a calibration spherical surface are shown. Also, we perform some corneal topography measurements.","PeriodicalId":212434,"journal":{"name":"SPIE Optical Systems Design","volume":"8 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2015-09-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131707610","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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